manual: Complete @standards in lang.texi.

	* manual/lang.texi (LDBL_MANT_DIG): Add annotation.
	(LDBL_DIG): Likewise.
	(LDBL_MIN_EXP): Likewise.
	(LDBL_MIN_10_EXP): Likewise.
	(LDBL_MAX_EXP): Likewise.
	(LDBL_MAX_10_EXP): Likewise.
	(LDBL_MAX): Likewise.
	(LDBL_MIN): Likewise.
	(LDBL_EPSILON): Likewise.
	(FLT_ROUNDS): Change standard from ISO to C90.
	(FLT_RADIX): Likewise.
	(FLT_MANT_DIG, DBL_MANT_DIG): Likewise.
	(FLT_DIG, DBL_DIG): Likewise.
	(FLT_MIN_EXP, DBL_MIN_EXP): Likewise.
	(FLT_MIN_10_EXP, DBL_MIN_10_EXP): Likewise.
	(FLT_MAX_EXP, DBL_MAX_EXP): Likewise.
	(FLT_MAX_10_EXP, DBL_MAX_10_EXP): Likewise.
	(FLT_MAX, DBL_MAX): Likewise.
	(FLT_MIN, DBL_MIN): Likewise.
	(FLT_EPSILON, DBL_EPSILON): Likewise.